The present invention relates to a photoconductor for electrophotography (hereinafter referred to as an "electrophotographic photoconductor" or simply as a "photoconductor"). Specifically, the present invention relates to an electrophotographic photoconductor that includes a photosensitive film containing organic materials on an electrically conductive substrate. The photoconductor is used in printers, copying machines and facsimiles which employ electrophotographic techniques.
It is necessary for photoconductors to retain surface charges in the dark, to generate electric charges in response to received light, and to transport the generated electric charges in response to the received light. Photoconductors may be classified into monolayered photoconductors, which have a layer that exhibits all the above described functions, and laminate-type photoconductors, which have a layer for charge generation and another layer for charge transport upon exposure to light and surface charge retention in the dark.
Conventional photoconductors employ the Carlson method for electrophotographic image formation. Image formation by the Carlson method includes the steps of charging the photoconductor in the dark by corona-discharge, forming electrostatic latent images of the original letters and pictures on the charged surface of the photoconductor, developing the electrostatic latent images with toner, and transferring the developed toner images to the carrier paper. The photoconductor is ready to be used again after steps of discharge, removal of residual toner and optical discharge are completed.
Inorganic photoconductive materials such as selenium, selenium alloys, zinc oxide and cadmium sulfide have been used as the photosensitive material for the above described photoconductors. The inorganic photoconductive materials are dispersed into a resin binder. Organic photoconductive materials such as poly-N-vinylcarbazole, 9,10-anthracenediolpolyester, hydrazone, stilbene, butadiene, benzidine, phthalocyanine and bisazo compounds have also been used as the photosensitive material for the above described photoconductors. The organic photoconductive materials are dispersed into a resin binder or deposited by vacuum deposition or by sublimation.
If necessary, various ingredients are added to the photosensitive film to improve the electrophotographic properties of the photoconductor. For example, German Patent No. 3 625 766 discloses phosphite compounds as phosphorous-containing additives. Althoughvarious additives have been examined to improve the stability of the photoconductor, a satisfactory effect has not been obtained to date.